Reconstruction of North American Drainage Basins and River Discharge Since the Last Glacial Maximum

Earth Surf. Dynam., 4, 831–869, 2016 www.earth-surf-dynam.net/4/831/2016/ doi:10.5194/esurf-4-831-2016 © Author(s) 2016. CC Attribution 3.0 License. Reconstruction of North American drainage basins and river discharge since the Last Glacial Maximum Andrew D. Wickert Department of Earth Sciences and Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN, USA Correspondence to: Andrew D. Wickert ([email protected]) Received: 1 February 2016 – Published in Earth Surf. Dynam. Discuss.: 17 February 2016 Revised: 6 October 2016 – Accepted: 12 October 2016 – Published: 8 November 2016 Abstract. Over the last glacial cycle, ice sheets and the resultant glacial isostatic adjustment (GIA) rearranged river systems. As these riverine threads that tied the ice sheets to the sea were stretched, severed, and restructured, they also shrank and swelled with the pulse of meltwater inputs and time-varying drainage basin areas, and some- times delivered enough meltwater to the oceans in the right places to influence global climate. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges, by combin- ing models of past ice sheets, glacial isostatic adjustment, and climate. The result is a time series of synthetic paleohydrographs and drainage basin maps from the Last Glacial Maximum to present for nine major drainage basins – the Mississippi, Rio Grande, Colorado, Columbia, Mackenzie, Hudson Bay, Saint Lawrence, Hudson, and Susquehanna/Chesapeake Bay. These are based on five published reconstructions of the North American ice sheets. I compare these maps with drainage reconstructions and discharge histories based on a review of obser- vational evidence, including river deposits and terraces, isotopic records, mineral provenance markers, glacial moraine histories, and evidence of ice stream and tunnel valley flow directions. The sharp boundaries of the reconstructed past drainage basins complement the flexurally smoothed GIA signal that is more often used to validate ice-sheet reconstructions, and provide a complementary framework to reduce nonuniqueness in model reconstructions of the North American ice-sheet complex. 1 Introduction therefore patterns of drainage-basin-scale water balance and river discharge to the oceans. At the time of Last Glacial Maximum (LGM) ice extent, Reconstructions of past ice-sheet thickness have prolif- ca. 30 to 19.5 ka (Clark et al., 2009; Lambeck et al., 2014), erated (e.g., Tushingham and Peltier, 1991; Marshall and North American drainage configurations and river discharge Clarke, 1999; Lambeck et al., 2002; Peltier, 2004; Tarasov were dramatically different from those at present. Ice ad- and Peltier, 2006; Tarasov et al., 2012; Gregoire et al., vance rerouted rivers (e.g., Ridge, 1997; Curry, 1998; Blu- 2012; Argus et al., 2014; Peltier et al., 2015), but are eval- mentritt et al., 2009), and ice streams fed temporarily en- uated using limited (Tarasov and Peltier, 2006; Tarasov larged drainage basins (Dyke and Prest, 1987; Patterson, et al., 2012) to no (all others) geologic evidence for past 1998; Margold et al., 2014, 2015). The growth of the drainage patterns. Most of these (all but Marshall and Clarke, ice sheets changed atmospheric circulation (Kutzbach and 1999, and Gregoire et al., 2012) were tuned or calibrated Wright, 1985; COHMAP members, 1988; Bromwich et al., to terminal moraine positions and records of glacial iso- 2004; Kim et al., 2008; Ullman et al., 2014) by generat- static adjustment, with the latter being a response with a ing up to 3.5–4 km of high-albedo ice-surface topography characteristic two-dimensional flexural half-wavelength of (e.g., Peltier, 2004; Tarasov et al., 2012; Peltier et al., 2015; 500–850 km over the high-flexural-rigidity Canadian Shield Ivanovic´ et al., 2016a) that influenced global climate and provence that was covered by the ice sheet (Vening Meinesz, Published by Copernicus Publications on behalf of the European Geosciences Union. 832 A. D. Wickert: North American deglacial water routing 1931; Kirby and Swain, 2009; Tesauro et al., 2012). G12 resentations of the modern drainage network wholly or par- (Gregoire et al., 2012), which is discussed in detail here, was tially in place of glacial-stage drainage basins (e.g., Blum built to roughly match ice-sheet outlines and evolve more et al., 2000; Sionneau et al., 2008; Montero-Serrano et al., freely. Additional geological data can help to constrain past 2009; Sionneau et al., 2010; Kujau et al., 2010; Lewis and ice-sheet geometries (see Stokes et al., 2015, who review and Teller, 2006; Tripsanas et al., 2007, 2014; Rittenour et al., motivate data–model integration efforts), but until now, sur- 2003, 2005, 2007; Knox, 2007) that help to propagate a face water flow paths have not been used to critically eval- lack of consciousness about the continental-scale hydrologic uate the suite of proposed past ice sheets. Flow-routing cal- changes that occurred, even in cases when the study acknowl- culations (e.g., Metz et al., 2011; Schwanghart and Scher- edges in the text that past drainage pathways were differ- ler, 2014) are deterministic and can be used to produce ent. The best current Cenozoic history of Mississippi River time series of drainage pathways predicted by each recon- drainage does not attempt to place its northern drainage basin structed ice sheet and its associated glacial isostatic adjust- boundary during the Pleistocene (Galloway et al., 2011). ment (GIA) history, forming the necessary links between Model-based studies likewise either test a range of possible each reconstructed ice sheet and measurable geomorphic drainage basin areas (Overeem et al., 2005) or assume that and sedimentary records. Furthermore, the discrete bound- the rivers have remained unchanged (Roberts et al., 2012). aries of drainage basins are sensitive to ice geometry in a In the former case, this can lead to less-precise calcu- way that is distinct from the broad and more diffuse GIA lations of sediment transport and deposition. In the lat- response, and therefore can provide a partly independent ter case, this violates the underlying assumptions used to check on the accuracy of any given ice-sheet reconstruction compute erosion and infer spatially distributed uplift. Pa- (Wickert et al., 2013). leoclimate general circulation model (GCM) reconstruc- On a global scale, climate change during deglacia- tions (e.g., Liu et al., 2009; He et al., 2013) maintain static tion may have been forced by meltwater delivery to drainage basins in spite of climate sensitivity to patterns of the oceans, especially at the time of the Younger Dryas meltwater routing (Condron and Winsor, 2012), and this has (e.g., Broecker et al., 1989). The global climate system is just begun to be addressed (Ivanovic´ et al., 2014, 2016a,b). highly sensitive to the locations of meltwater inputs to the All of these scenarios highlight the need for an improved oceans (e.g., Tarasov and Peltier, 2005; Murton et al., 2010; community-wide understanding of the ice-age effects on the Condron and Winsor, 2012; Carlson and Clark, 2012). Ge- continental-scale river systems of North America that pro- ologic data provide a timeline of meltwater delivery to one vides the necessary backdrop to understand the present-day basin or another (e.g., Ridge, 1997; Licciardi et al., 1999; rivers, their origins, and their evolution. Clark et al., 2001; Flower et al., 2004; Knox, 2007; Rittenour Here, I focus primarily on nine North American river et al., 2007; Carlson et al., 2009; Breckenridge and Johnson, basins. These are (counterclockwise from north) the Macken- 2009; Murton et al., 2010; Hoffman et al., 2012; Williams zie River, Columbia River, Colorado River, Rio Grande, Mis- et al., 2012; Breckenridge, 2015), with some types of data, sissippi River, Susquehanna River/Chesapeake Bay, Hud- such as oxygen isotopes, being able to be analyzed to pro- son River, Saint Lawrence River, and Hudson Bay/Hudson duce reconstructions of meltwater discharge (Moore et al., Strait. These catchments include those that were dramatically 2000; Carlson et al., 2007a; Carlson, 2009; Obbink et al., and directly impacted by Quaternary glaciation and those 2010; Wickert et al., 2013). The relationships between geo- that were far from the ice sheets, and together they consti- logical data in different parts of the continent must be con- tute a reasonably representative set of rivers from which the nected by conservation of ice-sheet mass and glaciological continental-scale hydrologic impact of glaciation on North continuity of ice flow. Continental-scale meltwater routing American drainage basins can be surmised. calculations that connect data and models address both of The present work is inspired by the dual and con- these concerns by using quantified ice-sheet thickness and nected needs for (1) an appropriate mapping tool for ensuring that water that is not sent to one basin is sent to data–model intercomparison and (2) maps of the past another. drainage basins of North America to inform geologic In general, there exists a lack of recognition of the im- studies. I first present a standardized and automated portance of Pleistocene drainage rearrangement on river sys- method to extract past drainage pathways and river dis- tems. In spite of the broad knowledge that river systems and charges from combinations of ice-sheet, GIA (Mitrovica drainage basins have changed significantly since the LGM and Milne, 2003; Kendall et al., 2005), and climate (Upham,

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